This invention relates to the field of foundry molding techniques. More particularly, it relates to the field of devices for reclaiming sand or similar granular material used in foundry molding. Reclamation of molding sand is highly desirable in view of the significant cost and high quality of the sand necessary for this purpose. By reclaiming this sand, significant reductions in cost and conservation of resources are obtained. To reclaim the sand it is necessary that it be reduced from lumps to single discrete grains and that trash, metallic particles and the like be removed therefrom. An additional treatment which must be performed on the sand grains is removal of the residual binder utilized in the molding process. Often these binders are organic resins or dead clay in the case of green sand in a clay bonding system.
Failure to remove sufficient amounts of the binder results in molds of insufficient strength if only reclaimed sand is utilized, or alternatively, it is necessary to continually add new sand to the reclaimed sand in order to obtain high strength molds if the binder is not adequately reduced.
It will be appreciated that one cubic foot of sand contains on the order of four hundred million sand grains and that it is therefore no simple task to obtain sufficient interfacial contact between the sand grains to produce a scrubbing action. According to the present invention, such interfacial scrubbing is obtained.
In the prior art, it has been known to provide devices for conditioning granular material, for example, U.S. Pat. No. 3,782,643 to Carpenter. In this device a centrifugal throwing wheel projects material horizontally outwardly therefrom for impact against a surface. The material rebounds from the surface downwardly to a collection trough. The Carpenter device does not produce a high density interfacial contact along the sand grains to reduce binder buildup due to the divergent paths of the sand grains. The grains once thrown outwardly by the wheel pass only briefly through the blast pattern before they fall to the collection trough.
It is accordingly an object of the present invention to provide an improved scrubbing method and apparatus for sand and similar granular material which greatly enhances the number of interparticle reactions to increase the effective removal of binder thereon.
It is another object of the present invention to provide a scrubbing method and apparatus for granular material in which the granular material returns along substantially the same path as it is dispensed to maximize interparticle reactions.
It is a further object of the present invention to provide a device which effects a two-stage scrubbing of granular material by movement of material between an impellor and control cage of the device prior to its being thrown from the impellor.
Other objects and advantages of the invention will become apparent from the remaining portions of the specification.